Total acidity determination direct titrations

The technique is generally unaffected by the state (ionic, imdissociated, sometimes complexed) of the analyte to be titrated. For example, the direct potentiometric determination of pH in a solution of a weak acid reports only the hydrogen ion concentration. Since the major portion of the acid is present in the undissociated form, direct potentiometry can not provide data yielding the total acid concentration. Potentiometric titration involves titrating the acid solution with a standard base, determining the equivalence point volume of standard base solution used, and calculating the total weak acid concentration from the stoichiometric data. 

Unsaponifled Fat. The Analytical Methods Committee of the S.A.C. recommends three determinations to obtain a correct indication of the total free fat or unsaponified saponifiable matter in soaps, (/) free fatty acids by direct titration as above, (m) unsaponified neutral fat and un-saponifiable matter by the method described below, (m) unsaponifiable matter by saponification and extraction of ( ). Hence the unsaponified neutral fat is it) — (m), and the total free fat or unsaponified saponifiable matter is (it) — iii) + (0 ... 

Various workers have discussed the determination of total alkalinity and carbonate [ 10-12], and the carbonate bicarbonate ratio [ 12] in seawater. A typical method utilises an autoanalyser. Total alkalinity (T milliequivelents per litre) is found by adding a known (excess) amount of hydrochloric acid and back titrating with sodium hydroxide solution a pH meter records directly and after differentiation is used to indicate the end-point. Total carbon dioxide (C milliequivelents per litre of HCO3 per litre) is determined by mixing the sample with dilute sulfuric acid and segmenting it with carbon dioxide-free air, so that the carbon dioxide in the sample is expelled into the air segments. The air... 

Samples for analysis often contain traces of other compounds, in addition to ascorbic acid, that reduce DCIP. One way to minimize the interference of other substances is to analyze two identical aliquots of the sample. One aliquot is titrated directly and the total content of all reducing substances present is determined. The second aliquot is treated with ascorbic acid oxidase to destroy ascorbic acid and then titrated with DCIP. The... 

When measuring acidity in foods and beverages there are two common units of measurement titratable acidity and pH. There is no direct relationship between pH and titratable acidity, therefore, both must be measured experimentally. Titratable acidity (TA), also referred to as total acidity, measures the total acid content in a food or beverage system and is determined by titration of the acids in the food system with a standard base. 

Permanent hardness can also be estimated by the alkalimetric method of Wartha and Pfeifer. A measured volume (200 e.e.) of the water is boiled with 50 c.e. of a mixture of decmormal solutions of sodium carbonate and hydroxide in equal amounts after restoring to the original volume and allowing the solution to settle, the residual alkali is determined by titration with standard acid. As the bicarbonates do not cause any consumption of alkali, there is a direct proportionality between the quantity of alkali which disappears and the total amount of sulphates and chlorides of calcium and magnesium. Sodium carbonate alone does not efficiently precipitate magnesium salts from solution, but precipitation as the hydroxide is complete if excess of sodium hydroxide is present it is for this reasoii that a mixture of sodium carbonate and hydroxide is applied 3 (see also p. 211). 

Acidity and Alkaline Reserve Measurements. Acidity was titrated directly with standard NaOH solution to determine total acid content. 

Numerous tertiary amines that also contain carboxylic acid groups form remarkably stable chelates with many metal ions. Ethylenediamine tetra-acetic acid (EDTA) can be used for determination of 40 elements by direct titration using metal-ion indicators for endpoint detection. Direct titration procedures are limited to metal ions that react rapidly with EDTA. Back titration procedures are useful for the analysis of cations that form very stable EDTA complexes and for which a satisfactory indicator is not available. EDTA is also used for determining water hardness the total concentration of calcium and magnesium expressed in terms of the calcium carbonate equivalent. 

Chemical analysis Chemical analyses on suspension or powder samples were performed by a volumetric method (0.05 normal potassium dichromate) following dissolution in hydrochloric acid. The ferrous (Fe2+) content was determined directly. The ferric (Fe3+) content was analyzed via the Zimmermann-Reinhardt (SnCl2 reduction) technique, which gives the total iron. Subtraction of the Fe2+ gives the desired Fe3+ value. The Fe2+/Fe3+ ratio was determined with an accuracy of 0.01. The accuracy of the determination of the total iron was 0.5% of the result. Chloride content was determined by Volhard titration with an accuracy of 5% of the result. Nitrogen content was analyzed with the Nessler method with a relative accuracy of 15%. 

Total SulfuT Dioxide After Alkali Treatment The fact that neutral sodium sulfite does not combine with carbonyl compounds and that the hydroxysulfonic acid compounds are rapidly decomposed on treatment with alkali was used by Ripper (1892) as the basis for the determination of total sulfur dioxide in wine by direct iodine titration. In his method, 50 ml. of wine were pipetted into a 200-ml. flask containing 25 ml. of 1 iV KOH. The mixture was shaken and allowed to stand for 10 to 15 minutes. Then 10 ml. of dilute sulfuric acid (1 + 3) were added, and the solution titrated rapidly with 0.02 N iodine solution to a starch end point which persisted for some time. This method was used as the ofiicial direct titration method for wine in the first edition (1919) of the A.O.A.C. Methods of Analysis in the third (1930) edition it was extended to white grape juice, wine, and similar products (1N NaOH or KOH was used and the solution during standing for 15 minutes was occasionally agitated) hut it was dropped from the fourth (1935) and succeeding editions. Ripper compared his method with the Haas distillation method on ten wines whose SO2 content varied from 42 to 1488 mg. per liter and found the difference between the two to vary from 0 to 5 mg. 

Combined Alkali.—The difference between total alkali and free alkali (caustic and carbonate together) represents the alkali combined with fatty acids. This figure may also be directly determined by titrating, with N/2 acid, the alcoholic solution of soap after the free caustic estimation, using lacmoid as indicator. 

Native polysaccharides with acid groups other than the uronic type are not very common except for the sulfate esters. Total acidity may be estimated by direct titration, but erroneous results are obtained if the polysaccharide is alkali-labile as is the case with many oxidized polysaccharides. Addition of calcium acetate (7, 8) or sodium bromide 8, 9) to the polysaccharide solution increases the accuracy of the titration. Other methods for the estimation of carboxyl and other acidic groups involve determination of the amount of methylene blue absorbed, or determination of the amount of silver salt formed by exchange from a solution which contains silver in combination with a very weak acid. The sulfate content of polysaccharide sulfates, such as agar, is obtained by ordinary sulfate analysis of the completely hydrolyzed or ashed polysaccharide. 

Direct titration after separation of the solids from the aqueous phase is another economical technique for on-site routine monitoring of total volatile acids in anaerobic processes. When utilizing this technique one should be aware of the imderlying assumptions in the different titration methodologies used. Some of the more complex titration methods with several endpoints can also determine alkalinity (system capacity to buffer acids) in addition to total VFA concentration [31]. Online titration systems have also been used successfully [32]. 

The total acidity, which includes other oxyacids of phosphorus (unlikely to be present in quantity, otherwise the acid would not pass the B.P.C, tests) can be titrated direct with alkali to methyl orange or bromophenol blue. 1 ml 0-5N = 0 03300 g. Hypophosphorous acid, after neutralisation may be determined by the methods described below for hypophosphites. 

Total acidity of the samples was determined by the reverse titration using n-butylamine solution in cyclohexane with bromthymol blue as an indicator. The strength of acid sites was estimated by direct titration with n-butylamine using Hammett indicators (Aldrich) benzalacetophenone (pKbh = -5.6), antraquinone (-8.2), 4-nitrotoluene (-11.35), l-chloro-3-nitrobenzene (-13.16), 2,4-dinitrotoluene (-13.75) and 2, 4-dinitro-l-fluorobenzene (-14.52). All samples were dried at 500°C, Ih before testing. XRD patterns of samples were recorded on DRON-4-07 diffractometer (CuKa radiation). Surface areas, pore size distributions and pore volumes were measured by N2 adsorption at 77 K using Nova 2200e Smface Area and Pore Size Analyzer. Before analysis, the samples were treated at 300°C under vacuum. 

The double titration method, which involves the use of ben2ylchloride, 1,2-dibromoethane, or aUyl bromide, determines carbon-bound lithium indirectly (101,102). One sample of the //-butyUithium is hydroly2ed directly, and the resulting alkalinity is determined. A second sample is treated with ben2ylchloride and is then hydroly2ed and titrated with acid. The second value (free base) is subtracted from the first (total base) to give a measure of the actual carbon-bound lithium present (active base). 

The oxidimetric method, which involves the use of soUd vanadium pentoxide as oxidant (103). The vanadium is reduced quantitatively by butyUithium and is determined potentiometricaUy by titration with standard sulfatoceric acid [17106-39-7]. This method gives a direct measure of the actual carbon-bound lithium present when compared to the total titrated alkalinity. 

Free Fatty Acids (as oleic acid) Using the diglyceride fraction under Total Glycerides (below), determine as directed under Free Fatty Acids, Appendix VII, except add 2 mL of phenolphthalein TS, and titrate with the appropriate normality of sodium hydroxide. Use the following equivalence factor (e) in the formula given in the procedure ... 

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